Your two EXTREMELY short whips configured as a horizontal dipole will have very high losses and low efficiency? because they are physically short. Even though the whips load the elements to achieve resonance their efficiency is going to be horrible. This is the price you pay for "convenient" short antennas at low frequencies. Remember SWR has nothing to do with how well an antenna can radiate or receive an RF signal. A 50 ohm resistor will give you a 1:1 SWR but it will be useless as an antenna.
I generated a very quick & dirty model of your antenna and for NVIS signals arriving from straight overhead the difference between a full-sized dipole and your two short whips at 12' is on the order of >20 dB. This is a huge difference so when you say it works like rubbish it is in fact working as it should.
Gedas, W8BYA EN70
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This is why some people appear bright until you hear them speak.
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On 3/10/2020 8:54 AM, nanovnauser@... wrote: hi all i have a 80m dipole set for 3.775 Mhz,it seems to work rubbish,ive just done some adjustments,,take a look at the pics of it on the vna,does it look ok,views welcome,cheers m3vuv.ps,forgot to say its 2 80m mobile whips in a dipole config,up at about 12 feet for nvis .
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On the whip - loading coils....
The (B)and(W)ith of an antenna is determined by it's (Q)uality factor, thus of the R L and C components that make an antenna:
L by the length of the whips
C by he surface of the whips
R defined by diameter and material of the whips
The quality factor of a combination of RLC is given by this formula
Q = 1/R *SQR(L/C)??? and BW=1/Q
Just like a resonance circuit . Note that this formula is more complex if you need real values; just for understanding.
A wire antenna with infinitely? thin wire? would have only L and no C because it has no surface to create capacitance.
the quotient of L/C is very high, and the BW will be very small
To increase bandwidth, add capacitance by using thick wire or even tubes, or add a plate at the end of the wire.
Increasing R will work also, but at the cost of signal losses by dissipation.
Gert Gremmen
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On 10-3-2020 15:57, Ronan Daly wrote: Using mobile whips it will be rubbish. Its not a dipole - its 2 loading coils
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Re: Dumb question: What are REAL, IMAG, and PHASE good for?
#general_vna
Well, now the answer is beyond dumb ;<))
If you put a signal on a coax, it will start traveling along, very fast but not infinity fast.
If it reaches the end of the cable there are 3 interesting cases:
1. the cable is shorted
2. the cable is open
3. that cable is characteristically terminated (most 50 or 75 Ohm)
(which is the same as if an infinitely long cable is connected to
the end)
Case 1: as the cable is shorted, the voltage at the end will be 0 all the time. So our signal arrives and gets REFLECTED and the polarity inverses.
that is where the -1 comes from.
Case 2 : as at the end of an open cable the current is always 0. So our signal arrives , gets REFLECTED and the polarity does NOT inverse.
that is where the +1 comes from
In case 3 the signal is simply dissipated in the resistor, and no reflection occurs
that is where the 0 comes from
Note that the values? -1 to +1 are_normalized_, this means that the real value of the signal is first divided by itself before being graphed.
A voltage of 800 mV will be divided by 800 to get a normalized value of 1
This explains the values in a smith graph on the horizontal axe only.
Jean-Roger: feel free to continue ?
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On 10-3-2020 16:01, F6EGK - Jean-Roger wrote: All explanations above are right. However there can be a confusion when looking at what is really displayed by the NanoVNA.
REAL and IMAG parameters are not the samething as RESISTANCE and REACTANCE parameters. REAL and IMAG apply to reflection coefficient ¦£, in its complex form (a+j.b). That's why values are always in the [-1,1] interval, without any associated unit. When REAL=-1 and IMAG=0, it is the Short circuit situation. When REAL=1 and IMAG=0, it is the Open circuit situation. When REAL=0 and IMAG=0, it is the normal Loaded (50 ohms) situation.
LINEAR is the ¦£ modulus form of combined REAL and IMAG values, and finally POLAR is the geometric representation of REAL, IMAG and PHASE values. When POLAR is displayed by the NanoVNA, and even if data values are exactly displayed as for Smith Chart, results must not be read in the same way. Have a try by displaying two CH0 traces, POLAR and SMITH.
SWR and LOGMAG (Return Loss) are derivated from ¦£ modulus (LINEAR). For educational purposes I have created an ods file (see below), showing and calculating NanoVNA parameters. You can play with it by entering values in the blue fields, and also checking what are the arithmetic relations behind the different results. Here Group Delay is not relevant as calculations are done for a discrete (CW) frequency.
A last word about the use of REAL and IMAG parameters. The following case (see attachment) is an opened coaxial cable (length 2 meters), creating a quarter wave stub (at red marker). An opened coaxial cable remains a good use case for education and increase of knowledge. On the NanoVNAsaver snapshot we see clearly that displayed values between RESISTANCE/REACTANCE and REAL/IMAG do not allow an immediate comparison. For example at red marker, R+jX or Smith Chart highlight a value of 0+j0 ohms (short circuit situation), and checking this with REAL/IMAG chart you get -1 (REAL) and 0 (IMAG) which is the same thing. Be careful with REAL and IMAG curves which follow sinus and cosinus rules, it reflects simply a monotonous variation of PHASE.
REAL is also interesting if you want to measure a coaxial cable length, thanks to advanced TDR function.
Sorry for possible english language mistakes.
73 from Jean-Roger / F6EGK
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I know its narrow band but just its for a spot frequency of 3.775Mhz,heres some more pics of it and screen shots of it on my foxdelta analyser.also a couple of pics of my verticle.73
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Re: Dumb question: What are REAL, IMAG, and PHASE good for?
#general_vna
All explanations above are right. However there can be a confusion when looking at what is really displayed by the NanoVNA.
REAL and IMAG parameters are not the samething as RESISTANCE and REACTANCE parameters. REAL and IMAG apply to reflection coefficient ¦£, in its complex form (a+j.b). That's why values are always in the [-1,1] interval, without any associated unit. When REAL=-1 and IMAG=0, it is the Short circuit situation. When REAL=1 and IMAG=0, it is the Open circuit situation. When REAL=0 and IMAG=0, it is the normal Loaded (50 ohms) situation.
LINEAR is the ¦£ modulus form of combined REAL and IMAG values, and finally POLAR is the geometric representation of REAL, IMAG and PHASE values. When POLAR is displayed by the NanoVNA, and even if data values are exactly displayed as for Smith Chart, results must not be read in the same way. Have a try by displaying two CH0 traces, POLAR and SMITH.
SWR and LOGMAG (Return Loss) are derivated from ¦£ modulus (LINEAR). For educational purposes I have created an ods file (see below), showing and calculating NanoVNA parameters. You can play with it by entering values in the blue fields, and also checking what are the arithmetic relations behind the different results. Here Group Delay is not relevant as calculations are done for a discrete (CW) frequency.
A last word about the use of REAL and IMAG parameters. The following case (see attachment) is an opened coaxial cable (length 2 meters), creating a quarter wave stub (at red marker). An opened coaxial cable remains a good use case for education and increase of knowledge. On the NanoVNAsaver snapshot we see clearly that displayed values between RESISTANCE/REACTANCE and REAL/IMAG do not allow an immediate comparison. For example at red marker, R+jX or Smith Chart highlight a value of 0+j0 ohms (short circuit situation), and checking this with REAL/IMAG chart you get -1 (REAL) and 0 (IMAG) which is the same thing. Be careful with REAL and IMAG curves which follow sinus and cosinus rules, it reflects simply a monotonous variation of PHASE.
REAL is also interesting if you want to measure a coaxial cable length, thanks to advanced TDR function.
Sorry for possible english language mistakes.
73 from Jean-Roger / F6EGK
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Using mobile whips it will be rubbish. Its not a dipole - its 2 loading coils
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A decent spectrum analyzer would need good image frequency (and spurs) suppression. And it would need a much faster ADC because a 5 or 10 KHz bandwidth is way too low to be useful. I need a real time spectrum analyzer that can capture at least 10 MHz of spectrum at once. In essence, a spectrum analyzer is more complicated than a vna. However, they have quite some hardware in common. It is on my wish list to design a decent 6 GHz VNA/SA combi, not a cost optimized VNA "toy" like all nanoVNA versions. But the wish list grows faster than I can handle...
Reinier
Op 10-3-2020 om 15:08 schreef Larry Rothman:
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Although, thinking about this a little more - there IS alot more space for enhanced firmware on the new V2 board which uses Analog Devices freq generator chips so additional functionality -might- be able to be developed for a spectrum analyser feature using the input port.The problem is the dynamic range and how to control input levels.
What do you think, Gabriel?
It would also be nice to have an option to flip the display 180 degrees.
Cheers,Larry
On Tuesday, March 10, 2020, 9:55:20 a.m. GMT-4, Larry Rothman <nlroth@...> wrote:
Not really worth it when there are countless RTL-SDR dongle projects that allow you to do this already on the cheap.
? ? On Tuesday, March 10, 2020, 9:49:26 a.m. GMT-4, nanovnauser@... <nanovnauser@...> wrote:
is there any plans to make a spectrum analyser along the same lines as the nanovna?,seems to me it would be a winner.
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Although, thinking about this a little more - there IS alot more space for enhanced firmware on the new V2 board which uses Analog Devices freq generator chips so additional functionality -might- be able to be developed for a spectrum analyser feature using the input port.The problem is the dynamic range and how to control input levels.
What do you think, Gabriel?
It would also be nice to have an option to flip the display 180 degrees.
Cheers,Larry
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On Tuesday, March 10, 2020, 9:55:20 a.m. GMT-4, Larry Rothman <nlroth@...> wrote:
Not really worth it when there are countless RTL-SDR dongle projects that allow you to do this already on the cheap.
? ? On Tuesday, March 10, 2020, 9:49:26 a.m. GMT-4, nanovnauser@... <nanovnauser@...> wrote:?
is there any plans to make a spectrum analyser along the same lines as the nanovna?,seems to me it would be a winner.
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Not really worth it when there are countless RTL-SDR dongle projects that allow you to do this already on the cheap.
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On Tuesday, March 10, 2020, 9:49:26 a.m. GMT-4, nanovnauser@... <nanovnauser@...> wrote:
is there any plans to make a spectrum analyser along the same lines as the nanovna?,seems to me it would be a winner.
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is there any plans to make a spectrum analyser along the same lines as the nanovna?,seems to me it would be a winner.
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On Tue, 10 Mar 2020 05:54:55 -0700, you wrote: hi all i have a 80m dipole set for 3.775 Mhz,it seems to work rubbish,ive just done some adjustments,,take a look at the pics of it on the vna,does it look ok,views welcome,cheers m3vuv.ps,forgot to say its 2 80m mobile whips in a dipole config,up at about 12 feet for nvis .
The first 2 pics look OK, but then you did something wrong to your VNA. Usually 80 m wire antennas are very narrow and cannot cover the complete 80m band. To make it broadband use multiple wire arrangements. OE8UWW
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Re: NanoVNA-H new user - can't connect to USB (windows 10)
Ive had this issue a few times on win 7 sp1,seems the windows updates screws the drivers up,normaly reinstall the st whatever it is driver and then it works,not sure on win 10 tho as i hate it with a vengance! 73.
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hi all i have a 80m dipole set for 3.775 Mhz,it seems to work rubbish,ive just done some adjustments,,take a look at the pics of it on the vna,does it look ok,views welcome,cheers m3vuv.ps,forgot to say its 2 80m mobile whips in a dipole config,up at about 12 feet for nvis .
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Re: LPF Conundrum -- Eureka...
The trace capacitance is ~ 6.5 pF before and after the modifications.
The inductance is 0.046 uH. Insignificant?
The PCB is small, 17mm x 25mm, not much trace area/length.
Allison, The only examples I found in EMRFD are for VHF filters on page 3.7...nothing for HF.
Still need to build the 30m filter...
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Chuck, W5USJ
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Re: NanoVNA-H new user - can't connect to USB (windows 10)
when I connect it to a laptop using the supplied USB-A to USB-C cable, I get a warning A bad cable is among the first things to suspect.
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Re: 70 MHz - 6 GHz spectrum analyser & tracking generator
From: Pierre Martel
Hi David,
Do you have some information about the maximum dynamic range the pluto can
do in sa/tg mode?
====================================
Pierre,
I've not seen any specifications for that, but here's a quick plot of the RTL-SDR 88-108 MHz bandstop filter compared with a Rigol DSA-815. I would reckon 60 dB at that frequency, and that's with the 10 dB attenuator on the Pluto TX and RX ports.
The plots were made some time apart. I looked on the RTL-SDR site for their response plot, but it seems to be missing....
Cheers,
David
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SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv
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Re: 70 MHz - 6 GHz spectrum analyser & tracking generator
From: Leif M
Are any these able to show close sidebands. Like what happens with 1kHz or 100Hz SSB modulation
================================
The minimum receiver bandwidth range is currently 2 MHz, but the Pluto can be used very successfully as a narrow-band receiver so I think this is just a programming limitation at the moment. You could buy the programmer (that's NOT me) a beer or two via PayPal along with with request for narrower receiver spans!
Cheers,
David
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv
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Re: NanoVNA-H new user - can't connect to USB (windows 10)
I have discovered that this happens and everyone tells you the problem has
been solved. But when you try all the fixes, it still does not work! It
seems that the WIN10 virtual comport gets confused by having made many
changes. I don't know exactly why, but I found a site that has a "driver
fixer" and that worked for me.
Here is a link:
Please let me know if this solves your problem too!
Robert M.
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On Mon, Mar 9, 2020 at 4:14 PM yah_ev <evan.tuer@...> wrote: Hi all,
I bought a new NanoVNA-H on ebay and received it today. It seems to work,
but when I connect it to a laptop using the supplied USB-A to USB-C cable,
I get a warning "USB device not recognised. The last USB device you
connected to this computer malfunctioned and Windows does not recognise
it". I've tried connecting many times, different ports, rebooting, and a
different laptop, but always get that message and the device shows up as
"not working" in device manager.
I had a quick look at the board, the connections to the socket and
soldering of the processor look OK, no shorts that I can see.
Has this been seen before, is there a solution or do I need to buy another
one?
Thanks for any advice.
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Re: Recommended battery type/size/specs for nanovna-v2?
Thanks, Dragan - clearly seen on the web page!
Parts ordered...
Dave
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Re: Recommended battery type/size/specs for nanovna-v2?
Recommended capacity and dimensions are listed on tindie page. On Tue, 10 Mar 2020 at 01:59, David Feldman < [email protected]> wrote: Please excuse this post if it's been covered previously, but with a
nanovna-v2 enroute via tindie, I realized I believe it is not fitted with a
battery by default. Is the battery specification (part number or dimension,
anda any specific additional requirements) available?
Thanks,
73 Dave WB0GAZ wb0gaz@...
(originator of nanovna-users on groups.io, so with precious little time
then left to actually play with the thing!)
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Chuck Carpenter
Oristo
David J Taylor
Robert Malsbury